In drilling and production operations for the extraction of liquid and/or gas assets from the Earth (for example, in the extraction of hydrocarbon fluids such as oil and natural gas), accuracy of measurement information indicating, e.g., a rate of flow of a fluid mixture upwards along a subterranean borehole or wellbore may be greatly dependent on the particular fluid flow conditions in the wellbore (or at different points along the which wellbore). A particular fluid flow measurement value, for example, indicative of rates of flow of a bubbly mixture along the wellbore, may vary dependent on a phase composition of the bubbly fluid mixture at the respective points of measurement.
Pressure and temperature conditions vary greatly along the wellbore, causing significant variation on fluid flow characteristics of different fluids and/or different fluid phases along the length of the borehole. Downhole pressures are usually sufficiently large that, for example, natural gas extracted via the wellbore are in the liquid phase for a portion of its flow along the wellbore, transitioning to the vapor phase (or gas phase, used synonymously herein) at a particular fluid pressure, temperature, and fluid composition, typically corresponding to a particular location (or bubble point) along the wellbore. When natural gas, for example, comes out of solution, significant cooling may occur due to the liquid-to-vapor phase change. This can cause freezing in some instances, particularly in subsea applications where the production of methane-water crystals, i.e. clathrate hydrates, can be problematic.
Fluid behavior is significantly dependent on the phase and composition of fluid flowing along the wellbore. Fluid flow measuring equipment may thus, e.g., provide flow rate measurements that are susceptible to misinterpretation based on inaccurate phase composition information.
Reliable interpretation of measured fluid flow parameters is thus, to some extent, dependent on accurate assessment of fluid composition at the location along the wellbore where the measurement was taken. Accurate measurement and/or monitoring of downhole fluid flow conditions, however, is typically complicated by significant wellbore depths, sometimes being located in remote locations, e.g., at off-shore drilling installations.